There is a recent trend in the laundry detergent manufacturing industry to provide laundry detergent powder that, upon dissolution with water, generates a wash liquor having a pH typically in the range of from 7.0 to 9.0. Conventional laundry detergent powders today, upon dissolution with water, provide a wash liquor pH in the range of 10.5-11.0, and sometimes higher. Whilst high a wash pH in these typical ranges provide good cleaning performances, it is difficult to provide fabric care benefits. In seeking to improve the fabric care performance of laundry detergent powder, detergent formulators are developing laundry powder that provides a low pH wash liquor. Typically, this necessitates the removal from the powder of bulk ingredients that provide alkalinity to the wash liquor. Such ingredients are typically carbonate salt such as sodium carbonate, and silicate salt, such as sodium silicate. These ingredients are often formulated into the laundry powder, not only to provide a wash liquour pH of ˜10.5, but also to provide good physical properties to the laundry powder.
The base particle of a laundry detergent powder is typically prepared by a spray-drying process. During this process, detergent ingredients such as detersive surfactant, polymer, filler salt if used, are formed into an aqueous mixture, often called a crutcher mix, and then spray-dried to form a spray-dried laundry detergent particle. This spray-dried particle can be used as a laundry detergent powder product, or (and more usually) the spray-dried particle is mixed with other ingredients such as bleach particles, enzyme particles, perfume, and sometimes additional surfactant particles and other dry-added particles like filler particles such as sodium sulphate particles, to form a fully formulated laundry detergent powder.
The presence of carbonate salt and silicate salt in the spray-dried base particle, provide not only the alkalinity typically used by the detergent formulator to provide good cleaning (˜10.5), but also provides good physical characteristics to the spray-dried base detergent particle. Such physical characteristics include good cake strength and good flowability.
However, recent moves to formulate laundry detergent powder, and hence also the spray-dried base detergent powder, at a lower pH, has led to the need to remove ingredients such as carbonate salt and silicate salt from the spray-dried base powder. This in turn has led to problems of poor physical properties in the spray-dried particles that are being developed for use in these low pH laundry powder products.
Ingredients such as silica have been considered as a replacement for the carbonate salt and silicate in the spray-dried particle. However, silica is difficult to handle during the manufacturing process. The very low density and small particle size of silica means complicated and elaborate processing equipment and controls will be needed in order to dose silica in a crutcher mix ahead of spray-drying the mixture to form the spray-dried base particle. The behavior of silica during its introduction into the crutcher mixture is often described as gaseous like, or smoke like, and creates many problems such as dusting, and accurate dosing.
The inventors have found that rather than introducing silica as a starting material and trying to dose it into the crutcher mixture, silica can instead be formed in-situ in the crutcher mixture by the reaction of zeolite, which under conditions of low pH forms silica in an aqueous environment. In order to do this, the pH of the crutcher mixture must be carefully controlled so as to cause this reaction to take place.
Zeolite use to be a conventional detergent ingredient that use to be used often in laundry detergent powders. The manufacturing processes and ways of incorporating zeolite into the crutcher mixture are well understood. Zeolite gained popularity as a laundry detergent powder chemistry during the move to nil-phosphate laundry detergent powders a number of decades ago. At that time, zeolite was used as a good replacement for phosphate builder, such as sodium tripolyphosphate (STPP), and the use of zeolite in laundry powder increased. Zeolite is considered to be a good detergent builder. However, over the last decade, the laundry powder manufacturers have moved towards low built laundry detergent powders, and the use of zeolite in laundry powders has significantly decreased.
Instead of re-introducing zeolite into the spray-dried powder, the inventors have found that zeolite can be used as a substrate to form silica in-situ during the spray-drying process. The zeolite converts to silica, and the resultant spray-dried laundry particles are suitable for use not only in low pH laundry powders, but also in low built laundry powder. Since the zeolite converts to silica during the manufacturing process, the resultant particle also has the dispensing, dissolution and good fabric residue performance profiles of a low built laundry detergent powder.
This process provides a means to produce a spray-dried particle that can be used to formulate a low pH laundry powder, that benefits from the presence of silica, such as good physical characteristics, but without having all of the problems associated with trying to dose silica as a starting ingredient directly into the crutcher mixture. In addition, the particles produced by this process also have good dispensing, dissolution and good fabric residue performance profiles.